Silicoaluminophosphate molecular sieves exhibit a wide variety of framework types and are useful as catalysts in a variety of reactions. There are a wide variety of SAPO molecular sieves known in the art, of these the more important examples include SAPO-5, SAPO-11, SAPO-18, SAPO-34, SAPO-35, SAPO-41, and SAPO-56. Of particular interest are [Si—Al—P]-AEL (SAPO-11) and [Si—Al—P]-CHA (SAPO-34) both of which are of commercial interest. For the methanol-to-olefins process SAPO molecular sieves having the CHA framework type (“Atlas of Zeolite Framework Types”, 2001, 5th Edition, p. 96) and especially SAPO-34 are particularly important catalysts. The CHA framework type has a double six-ring structure in an ABC stacking arrangement. The pore openings of the structure are defined by eight member rings that have a diameter of about 4.0 Å, and cylindrical cages within the structure of approximately 10×6.7 Å. Other SAPO molecular sieves of CHA framework type include SAPO-44, SAPO-47 and ZYT-6. The AEL framework type SAPO-11 has a 1-D, 10 ring structure. It is known that SAPO-11 molecular sieves catalyse hydroisomerization reactions of wax with high selectivity yielding lubricants with high viscosity index and low pore point. SAPO-11 has also been found to be useful as a catalyst in naphtha cracking where it is found to give a high selectivity for propylene.
The synthesis of SAPO molecular sieves is a complicated process. There are a number of variables that need to be controlled in order to optimise the synthesis in terms of purity, yield and quality of the SAPO molecular sieve produced. A particularly important variable is the choice of synthesis template, which usually determines which SAPO framework type is obtained from the synthesis. U.S. Pat. No. 4,310,440 (Wilson et al.) teaches that “not all templating agents suitably employed in the preparation of certain species . . . are suitable for the preparation of all members of the generic class.” It is also well known that the same template may induce the formation of different framework types.
In U.S. Pat. No. 4,440,871 (Lok et.al) the synthesis of a wide variety of SAPO materials of various framework types are described with a number of specific examples. Also disclosed are a large number of possible organic templates, with some specific examples. In the specific examples a number of CHA framework type materials are described. SAPO-34 of CHA framework type is prepared utilising tetraethylammonium hydroxide (TEAOH), or isopropylamine, or mixtures of TEAOH and dipropylamine (DPA). This is believed to be the first reported synthesis of a SAPO-34 of CHA framework type. Also disclosed in this patent is a specific example that uses cyclohexylamine in the preparation of SAPO-44, also having the CHA framework type. Although other template materials are described in this reference there are no other templates indicated as being suitable for preparing SAPO's of CHA framework type. Certain aminoalcohols are also mentioned amongst the list of templates, including; triethanolamine, N-methyldiethanolamine, N-methylethanolamine, N,N-dimethylethanolamine and N,N-diethylethanolamine. Of these materials N,N-diethylethanolamine is shown to produce SAPO-5, which is of AFI framework type. For the other aminoalcohols no indication is provided as to which SAPO or which framework type may be obtained through their use. Also disclosed in this patent is the synthesis of SAPO-11 which is achieved through the use of di-isopropylamine, di-n-propylamine, and tetrabutylammoniumhydroxide, at crystallization temperatures of between 150° C. and 200° C.
Since the synthesis of SAPO-34 was reported in U.S. Pat. No. 4,440,871, tetraethylammonium hydroxide (TEAOH) either alone, or in combination with dipropylamine (DPA), has been the template of choice for preparing SAPO-34. However, there are problems associated with the use of TEAOH and DPA. When used alone, TEAOH affords a limited range of synthesis parameters. For example, under certain conditions TEAOH will also template the synthesis of SAPO-18 which has the AEI framework type. TEAOH is thus relatively intolerant to synthesis condition variations. TEAOH is sometimes combined with DPA. However, DPA has a low boiling point (110° C.) resulting in the need for production plants that can handle high pressures. In certain countries, the use of DPA requires special regulatory authorizations due to its toxicity. Also, DPA is an aggressive template and is often implicated in re-dissolution of the silicoaluminophosphate molecular sieve during its synthesis, resulting in poor quality crystalline product due to surface pitting of the crystals. Although there are problems associated with TEAOH and DPA, no completely satisfactory alternative template materials have been reported yet for the preparation of silicoaluminophosphate molecular sieves with the CHA framework type.
In U.S. Pat. No. 4,440,871, it was reported that SAPO-44 was obtained “as the major phase” using cyclohexylamine as template. In U.S. Pat. No. 6,162,415 (Liu, et.al.), relatively pure CHA SAPO-44 was obtained using the same template but with control of the ratio of template to aluminium component and the ratio of phosphorous component to aluminium component.
In U.S. Pat. No. 4,801,743 (Flannigan, et.al.), SAPO-11 was prepared using diethanolamine or diethanolamine in combination with dipropylamine as organic template at a crystallization temperature of 150° C.
In European Patent Publication No. 0,993,867, it was reported that the use of methylbutylamine resulted in SAPO-47 and the use of cyclohexylamine resulted in impure SAPO-44. Methylbutylamine has an even lower boiling point, at 91° C., than DPA. In U.S. Pat. No. 6,162,415 (Liu, et.al.), relatively pure SAPO-44 was obtained using cyclohexylamine as the template with additional control of the ratio of template to aluminium component and the ratio of phosphorous component to aluminium component.
In U.S. Pat. No. 5,096,684 (Guth et.al.), morpholine and tetraethylammonium hydroxide were found to be effective in the synthesis of SAPO-34 when in the presence of HF. Whilst this is an alternative to TEAOH or TEAOH/DPA mixtures, it requires the use of HF. This patent also discloses the preparation of SAPO-11 using di-n-propylamine as template in combination with HF at a crystallization temperature of 170° C.
When attempts have been made to utilise other types of template compounds such as aminoalcohols, silicoaluminophosphates of framework type other than CHA have been obtained. In U.S. Pat. No. 4,440,871 (Lok, et al) it was disclosed that the use of diethylethanolamine produced SAPO-5 (AFI). In U.S. Pat. No. 4,861,739 (Pellet, et al.) it was reported that the use of diethylethanolamine produced CHA SAPO-47. In U.S. Pat. No. 5,096,684 (Guth et.al.), N,N-diethylethanolamine was found, in the presence of HF, to produce SAPO-5, which is of AFI framework type. In U.S. Pat. No. 4,310,440 (Wilson et.al), triethanolamine, N,N-dimethylethanolamine, N,N-diethylethanolamine, N-methyldiethanolamine, and N-methylethanolamine, were all used to prepare AlPO4-5, aluminophosphates of AFI framework type. In European Patent Publication No. 0,993,867, it was reported that diethanolamine produced SAPO-34 and SAPO-5 with different levels of template in the synthesis mixture. To-date all attempts to reproduce SAPO-34 using this template have failed. In U.S. Pat. No. 4,310,440 (Wilson et al.) it was reported that N-methylethanolamine resulted in the formation of AlPO4-21 of AWO framework type.
In the art various attempts have been made to synthesizeAlPO4 or SAPO molecular sieves using templates based on the alkylene diamine or polyamine structures such as for example those based on for example ethylenediamine, 1,3-propanediamine, and 1,6-hexanediamine. In European Patent Publication No. 0,043,562, it was reported that the use of N,N,N′,N′-tetramethyl ethylenediamine as organic template resulted in the formation of AlPO4-21. In European Patent Publication No. 0,538,958, it was reported that the use of N,N,N′,N′-tetramethyl ethylenediamine as organic template resulted in the formation of an AlPO4 referred to as SCS-24. In European Patent Publication No. 1,142,833, it was reported that the use of N,N,N′,N′-tetramethyl-1,6-hexanediamine as organic template resulted in the formation of MeAPSO-56 and SAPO-56. In U.S. Pat. No. 4,898,660 (Wilson et.al), ethylenediamine was used to prepare AlPO4-12. N,N,N′,N′-tetramethyl-propane-1,3-diamine and N,N,N′,N′-tetramethyl ethylenediamine were reported to produce AlPO4-21. In U.S. Pat. No. 5,370,851 (Wilson), it was reported that the use of N,N,N′,N′-tetramethyl-1,6-hexanediamine as organic template resulted in the formation of SAPO-56. In U.S. Pat. No. 5,232,683 (Clark et.al.), it was reported that the use of 1,8-diaminooctane, 1,10-diaminodecane and 1,12-diaminododecane as organic templates resulted in the formation SCS-22 type aluminophosphate molecular sieves. Wilson, et al., have reported the use of N,N,N′,N′ -tetramethyl-1,6-hexanediamine as organic template resulted in the formation of AlPO-17, SAPO-17, MAPSO-34 and SAPO-56 (Microporous and Mesoporous Materials, 28(1), 125-137, 1999 and Studies in Surface Science and Catalysis (1995) 98, (Zeolite Science 1994: Recent Progress and Discussions), 9-10). Bu, et.al., have reported the use of, N,N,N′,N′-tetramethylethylenediamine and 1,3-diaminopropane as structure directing agents for the formation of cobalt aluminophosphates UCSB-4 and UCSB-5 (Microporous and Mesoporous Materials, 25(1-3), 109-117,1998).
Feng, et.al., have reported that a variety of cobalt phosphates having zeolite like structures could be prepared using a variety of alkylenediamines as structure directing agents (Nature (London), 388(6644), 735-741, 1997). In a latter work it was reported that cobalt aluminophosphates of CHA framework type could be prepared using N,N,N′,N′-tetramethyl-1,6-hexanediamine as organic template and a zinc aluminophosphate of CHA framework type could be prepared using N,N,N′,N′-tetramethyl-1,3-butanediamine as organic template or dibutylamine (Microporous and Mesoporous Materials, 23, 221-229,1998). Ferey, et.al., have reported that the use of N,N,N′,N′-tetramethyl-1,6-hexanediamine as organic template in the presence of ammonium fluoride produced AlPO-CJ2 (Journal of Solid State Chemistry 105(1), 179-90, 1993). Long, et.al., have reported that the use of N,N,N′,N′-tetramethyl ethylenediamine as organic template resulted in the formation of an AlPO4-21 and an AlPO4 molecular sieve named CFAP-2 (Chemical Journal of Chinese Universities 7(2), 100-4, 1986 and Journal of Fudan University (Natural Science) 25(3), 301-8, 1986). Tian, et.al., have reported that the use of N,N,N′,N′-tetramethyl-1,6-hexanediamine as organic template resulted in the formation of SAPO-56 and MAPSO-56 molecular sieves (Studies in Surface Science and Catalysis (2001), 135 (Zeolites and Mesoporous Materials at the Dawn of the 21st Century), 891-898 and Chemical Journal of Chinese Universities 22(6), 991-994, 2001).
In Chinese Patent No. 1,299,776, it was reported that the use of N,N,N′,N′-tetramethyl-1,6-hexanediamine as organic template resulted in the formation of SAPO-56 molecular sieve. In Chinese Patent No. 1,301,598, it was reported that the use of N,N,N′,N′-tetramethyl-1,6-hexanediamine as organic template resulted in the formation of SAPO-56, and various MeAPSO-56 molecular sieves. In U.S. Pat. Nos. 5,232,683, 5,879,655 and 5,514,362 (Miller), it was reported that SAPO-11 could be prepared using DPA as organic template at crystallization temperatures of >180° C. and typically between 190° C. and 200° C.
As can bee seen from the disclosures described herein, there have been a number of attempts to utilise alternative synthesis templates for the synthesis of silicoaluminophosphates and in particular silicoaluminophosphates of the AEL and CHA framework types. Many of these synthetic methods have limitations and it is desirable therefore to find new synthesis templates that are specific for the synthesis of silicoaluminophosphate molecular sieves of the AEL and/or CHA framework types. In addition there is a need in relation to [Si—Al—P]-AEL (SAPO-11) to find new templating systems which afford crystallization at low temperatures.
A further property of silicoaluminophosphates which is of interest is the morphology of the molecular sieve particles recovered from the synthetic process. In the case of SAPO-11 a highly desirable morphology is a platelet morphology in which the dimension of the crystal plane parallel to the direction of the D-1 channel is relatively thin. Typically, such morphologies are relatively difficult to achieve and often require the use of surfactants or other crystal modifiers. Alternative organic templates which enable such morphologies to be obtained with ease and ideally without the need to use additional surfactants and/or crystal modifiers are highly desirable.